Referring to FIG. 17, an organic EL device is formed by forming anodes 2 of ITO, a hole-carrying layer 3, an organic layer (light-emitting layer) 4, an electron-carrying layer 5 and cathodes 6 in that order on a surface of a transparent substrate 1, such as a glass plate. The organic layer 4 is of a high-molecular type or a low-molecular type. Some organic EL devices are of a passive driving system and others are of an active driving system. The low-molecular organic layers of organic EL devices of a passive driving type and those of an active driving type, and the cathodes 6 of the organic EL devices of a passive driving system are formed by vacuum evaporation. A metal mask 8 as shown in FIG. 18 is used in forming the low-molecular organic layer and the cathode electrodes in a desired pattern by vacuum evaporation. The metal mask 8 has a screen part 8A provided with fine slits arranged at small intervals and corresponding to regions in which a material is to be deposited. In some cases, a cathode separator method (JP8-315981A) is used for forming the cathodes in a desired pattern by vacuum evaporation.
All the foregoing prior arts have problems. When the metal mask is used, the metal mask 8 is simply placed on a surface to be subjected to vacuum evaporation of a substrate, and the metal mask 8 is held in place by the magnetic attraction of a magnet disposed on the back surface of the substrate. Since the screen part 8A of the mask 8 has a very low rigidity, the slits of the screen part 8A is liable to be distorted in holding the metal mask on the surface of the substrate. Particularly, when the slits are very fine, the slits cannot be maintained in a desired accuracy and, consequently, highly accurate patterning cannot be achieved. Since the prior art metal mask 8 has only the single screen part 8A, only one substrate can be processed by each vacuum evaporation process, which reduces productivity. The cathode separator method adjusts exposure in photolithography to form partition walls having inclined side walls and hence stable manufacture is difficult. (The electrodes cannot be separated if the taper of the partition walls having the shape of an inverted trapezoid is small, and the partition walls fall down if the taper of the partition walls is large.)